Some conditions of the spine result from degradation or injury to the bone structures, e.g., the vertebral bodies, of the spine. These conditions may be the result of bone degeneration such as by osteoporosis or trauma, or by injuries such as compression fractures. Any of these maladies can cause great pain.
Other ailments of the spine result in degeneration of the spinal disc in the intervertebral space between the vertebral bodies. These include degenerative disc disease and traumatic injuries. In any case, disc degeneration can cause pain and other complications. That deformation is commonly known as a herniated or “slipped” disc. The protrusion may press upon one or more of the spinal nerves exiting the vertebral canal through the partially obstructed foramen, causing pain or paralysis in the area of the spinal nerve's influence. Conservative treatment can include non-operative treatment requiring patients to adjust their lifestyles and submit to pain relievers and a level of underlying pain. Operative treatment options include disc removal. This can relieve pain in the short term, but also often increases the risk of long-term problems and can result in motor and sensory deficiencies resulting from the surgery. Disc removal and more generally disc degeneration disease are likely to lead to a need for surgical treatment in subsequent years. The fusion or fixation will minimize or substantially eliminate relative motion between the fixed or fused vertebrae. In surgical treatments, adjacent vertebra may be fixated or fused to each other using devices or bone grafts. These may include, for example, screw and rod systems, interbody spacers, threaded fusion cages and the like.
Some fixation or fusion devices are attached to the vertebra from the posterior side. Such devices protrude from the back and require hardware for separate attachment to each vertebra. Fusion cages and allografts are contained within the intervertebral space, but must be inserted into the intervertebral space in the same dimensions as desired to occupy the intervertebral space. This requires that an opening sufficient to allow the cage or graft must be created through surrounding tissue to permit the cage or graft to be inserted into the intervertebral space.
The described implants are suitable for fusing adjacent vertebrae where at least a portion of the natural disc between those vertebrae has been removed but are introduced into the volume at a small profile that is expanded to a larger profile after placement.
Human vertebral bodies have a hard outer shell of compacted, dense cortical bone (sometimes referred to as the “cortex”) and a relatively softer, inner mass of cancellous bone. Just below the cortex adjacent the disc is a region of bone referred to as the “subchondral zone.” The outer shell of compact bone (the bony endplate) adjacent to the spinal disc and the underlying subchondral zone are often referred to as the bony “end plate region.” The endplate region is the densest bone available to support a fusion implant. Removal of or compromise of, the endplate region by preparing the bone surface, e.g., by cutting into or boring into the cortex, allows implants to contact the softer and less dense cancellous bone that lies beneath the endplate. It is desirable to maintain the integrity of the cortex, if possible, in implanting fusion devices.
Complicating this desire to maintain the integrity of the vertebral bone surface adjacent the disc is the fact that that surface is somewhat dome-shaped. Such a dome-shaped surface does not always provide a predictable surface upon which to situate a fusion device. Additionally, many maladies related to discs cause the situations requiring distraction of the discs as part of the treatment. This means that the space between vertebrae is small.
There are a variety of implants for spinal fusion in current use.
One such implant has a modified cylindrical or tapered cylindrical shape. Implantation of such an implant requires a drilling step to create an adequate opening into the intervertebral space and a bore across the faces of the endplates. Since the surfaces of the upper and lower vertebral bodies adjacent the disc space are dome-shaped, some additional consideration must be given to gaining adequate contact between the vertebral bodies and the implant to achieve fusion.
One solution is shown in U.S. Publ. Appl. No. 2006/0241774, to Attali et al, in which a cylindrical plug is inserted into a bore in the intervertebral space and then expanded.
Non-cylindrical implants that are pushed into the disc space after a discectomy are also known. Although these push-in implants do have the advantage of supporting the adjacent vertebral bodies by contacting a substantial portion of the vertebral endplates, they do not offer the advantages associated with threaded cylindrical implants that are screwed into a bore in the adjacent vertebral bodies to more securely hold these implants in their final fully seated positions. Further, unless the endplate is at least partially decorticated, i.e. worked upon to access the vascularity deep to the outer most aspect of the endplate itself, fusion will not occur.
The implants are suitable as actors in vertebroplasty. Vertebroplasty is an image-guided, minimally invasive, nonsurgical, distractive, therapy used to strengthen broken vertebrae, whether the vertebrae are weakened by disease, such as osteoporosis or cancer, or fractured by stress.
Spinal fusion and vertebroplasty procedures often include a step of injecting an orthopedic cement mixture into the intervertebral space or into the fractured bone. The cement mixture may contain particulate osteogenic materials, e.g., mixtures of one or several calcium phosphate powders that react with water to form other calcium phosphate compounds, often an apatite, or others listed below. These cement mixtures are quite viscous and are difficult to inject through small diameter openings. Providing large passageways through the implant allows passage of the cement through the implant.
None of the cited documents disclose the described deformable implant.